Our objective is to define the molecular basis by which membrane glycoproteins are directionally transported to specific cellular locations. These investigations will be carried out using viral glycoproteins which are transported to different plasma membrane domains on surfaces of polarized epithelial cells. To identify sorting signals responsible for the directional transport of glycoproteins, we will analyze the effects of specific modifications and sequence substitutions on determining the cellular location of the resulting molecules. These studies will be carried out with viral glycoproteins which exhibit distinct orientations and transmembrane topology: the gp70/p15E glycoprotein of murine leukemia viruses, a bitopic membrane glycoprotein with a cleaved signal sequence that is anchored by hydrophobic residues near the C-terminus of the molecule, and the gPr-gag glycoprotein which is likely to be anchored to membranes in the opposite orientation. In order to characterize the intracellular transport pathway of MuLV glycoproteins, we will use specific antisera to identify transport vesicles involved in movement of glycoproteins from the Golgi complex to the plasma membrane. We will determine whether the two MuLV-encoded glycoproteins gp70/p15E and gPr-gag are present in the same population of transport vesicles and whether they are associated with one another on the plasma membrane. To further define the viral components which are involved in determining the maturation site of retroviruses in epithelial cells, we will investigate the site of virus assembly and release in cells which produce viral cores in the absence of viral glycoproteins, and determine the effects of supplementing these cells with viral glycoproteins directed to either the apical or basolateral membranes. In addition to providing a better understanding of basic cellular processes, the proposed studies should contribute to our knowledge concerning the pathogenesis of viral infections by elucidating the mechanisms by which viral components are targeted to particular locations.